We are basically interested in structural and functional aspects of higher organism chromosomes at the molecular level. The organism of the choice in this proposal is Drosophila nasutoides which has an unusually large autosome pair of highly heterochromatic nature. Its nuclear DNA shows four major satellite components amounting to 60% of the total genome. All of them are localized in this large heterochromatic chromosome. Our research plans, in general, revolve around the molecular organization of this particular heterochromatic chromosome. We propose to investigate the sequence organizations in some of these satellites, the structure of chromatins containing satellite sequences and the intereactions between these DNA components and certain chromosomal proteins. Research plans are outlined as follows: (1) Comprehensive survey on digestion patterns of satellite DNAs by various restriction endonucleases. Results of these experiments will be used for isolation of satellite chromatins and evolutionary studies on sequence divergence of satellites below. (2) Isolation of chromatins containing particular satellite sequences by using restriction endonucleases. These purified chromatin preparations will be used for the study of nucleosome arrangements in satellite chromatins by nuclease digestion and electron microscopy. From DNA cross-linking studies we obtained an evidence that satellite chromatins have fewer nucleosomes per given length of chromatin compared to the main band DNA chromatin. (3) Isolation and characterization of satellite sequence specific proteins and their role in heterochromatin structure. A specificity of such a protein will be determined by cytological technique using fluorescent antibody (4) Evolutionary divergence studies of satellite II. This satellite has 17% base-pair mismatching between repeat units and is digested by Sal I, Eco RI and Alu I, resulting in multimeric sizes. We will investigate how these sensitive sites are arranged with respect to each other. (5) Fluorescence studies of satellite DNAs and satellite chromatins. Fluorescent behaviors of quinacrine and Hoechst 33258 are examined and the results will be related to fluorescent bands seen in the large heterochromatic chromosome.